Diseased or otherwise deficient heart valves can be repaired or replaced using a variety of different types of heart valve surgeries. One general type of heart valve surgery involves an open-heart surgical procedure that is conducted under general anesthesia, during which the heart is stopped and blood flow is controlled by a heart-lung bypass machine. This type of valve surgery is highly invasive and exposes the patient to a number of potential risks, such as infection, stroke, renal failure, and adverse effects associated with use of the heart-lung machine, for example.
Due to the drawbacks of open-heart surgical procedures, there has been an increased interest in minimally invasive and percutaneous replacement of cardiac valves. Such surgical techniques involve making a relatively small opening in the skin of the patient, thereby providing access to the vascular system. A valve assembly may then be inserted into the patient and delivered to the heart via a delivery device similar to a catheter. This technique is often preferable to more invasive forms of surgery, such as the open-heart surgical procedure described above.
Various types and configurations of prosthetic heart valves are used in percutaneous valve procedures to replace diseased natural human heart valves. The actual shape and configuration of any particular prosthetic heart valve is dependent to some extent upon the valve being replaced (i.e., mitral valve, tricuspid valve, aortic valve, or pulmonary valve). In general, prosthetic heart valve designs attempt to replicate the function of the valve being replaced and thus will include valve leaflet-like structures. These leaflet-like structures can be used with heart valve bioprostheses, which involves using a natural valve material (e.g., a porcine valve) to make a heart valve. More specifically, these bioprosthetic replacement valves include a valved segment that is mounted in some manner within an expandable stent or frame structure to make a valved stent. In order to prepare such a valve for percutaneous implantation, one type of valved stent can be initially provided in an expanded or uncrimped condition, then crimped or compressed around a balloon portion of a catheter until it is as close to the diameter of the catheter as possible. When it is desired to expand the stent, such as when the stent is at its desired implantation location, the balloon is inflated to provide a certain outward radial force to achieve a particular stent expansion. In other percutaneous implantation systems, the stent of the valved stent can be made of a self-expanding material. With these systems, the valved stent is crimped down to a desired size and held in that compressed state within a sheath, for example. Retracting the sheath from this valved stent allows the stent to expand to a larger diameter, such as when the valved stent is in a desired position within a patient. With either of these types of percutaneous stent delivery systems, conventional sewing of the prosthetic heart valve to the patient's native tissue is typically not necessary.
Although there have been advances in percutaneous valve replacement techniques and devices, there is a continued desire to provide different stent or frame structures and delivery systems for delivering cardiac valves to an implantation site in a minimally invasive and percutaneous manner. There is also a continued desire to be able to control the inflow side of a valve during the implantation process to control the accuracy of placement within the body.